PB1883: TIME-LIMITED TREATMENT WITH ACALABRUTINIB PLUS OBINOTUZUMAB IN TREATMENT-NAÏVE CHRONIC LYMPHOCYTIC LEUKEMIA PATIENTS INDUCES DEEP REMISSIONS: EARLY RESULTS OF AN ONGOING PHASE 2 TRIAL.
Authors: J. Burger, M. Sivina, E. Kim, G. Issa, W. Wierda, N. Jain, P. Thompson, A. Ferrajoli
Journal: HemaSphere (2022)

Background: The Bruton’s tyrosine kinase (BTK) inhibitor acalabrutinib is approved for treatment of chronic lymphocytic leukemia(CLL). Acalabrutinib induces durable remissions in most CLL patients, which mostly are partial remissions (PR), and therefore treatment typically is given as long-term monotherapy. As a potential alternative we developed a time-limited regimen, combining acalabrutinib with obinutuzumab. Aims: Here, we report early results from 14 treatment-naïve patients with CLL who enrolled in this ongoing phase 2 trial (NCT04505254) since September, 2020 at MD Anderson Cancer Center. Methods: Patients and Study Design: Treatment-naïve CLL patients requiring therapy as per iwCLL criteria receive acalabrutinib 100 mg orally twice a day for 24 cycles, combined with monthly obinotuzumab for 6 doses, starting in cycle 3. The first dose of obinutuzumab is divided into 100 mg on day 1 and 900 mg on day 2 of cycle 3; 1000 mg are given during subsequent cycles (cycles 4-8). Patients who do not achieve a complete remission (CR) after cycle 8 can receive an additional 6 monthly doses of obinotuzumab during cycles 9 -14. Treatment is discontinued after 24 cycles, and patients will be monitored. The primary objective is to determine the durability of remissions after treatment discontinuation, secondary objectives are to determine clinical and laboratory characteristics that predict for early versus late relapse after time-limited therapy. Results: The median age of the patients is 70 yrs (range, 40 -83 yrs), 14% had del17p or TP53 mutation, 43% had an unmutated IgHV and 71% advance stage disease (RAI stage III and IV). The median baseline absolute lymphocyte count (ALC) and b2 microglobulin at start of therapy were 39.2x109/L (range: 7.1 – 188.4 x 109/L) and 4.2 mg/L (range: 2.2 – 7.9 mg/L), respectively. After a median follow-up of 7 months (2 – 16 months), 13 (93%) of patients remain on study; one patient died (7%) due from complications from a presumed bacterial (COVID19-negative) pneumonia after 2 months on therapy. The estimated one-year PFS and OS for the cohort is 92.8 %. Seven patients were evaluable for response assessment after 8 months of therapy. No patient has yet discontinued therapy. All patients achieved a PR (one patient with undetectable minimal residual disease/U-MRD in the bone marrow), accounting for an overall responsonse rate of 100%. The median levels of bone marrow infiltration by CLL cells, quantified by flow cytometry, declined from 83.6% (range: 54.3 – 94.0 %) at baseline to 4.1% (range, 0.0 - 63.3%, n=7, p<0.05, see figure) after 6 cycles of combination treatment. Sixty-four percent of patients completed all doses of obinotuzumab, 50% requiered a dose reduction of acalabrutinib to 100 mg per day due to adverse events (AE). Grade 33 AE were observed in 4 patients (29%), which included decreased neutrophil counts (n=2), syncope (n=1), and grade 5 lung infection (COVID19 not detected, n=1). The most frequently reported non-serious related AE (3 2 patients) were anemia (n=5 [36%]), decreased platelets counts (n=3 [21%]), bruising (n=3 [21%]), limbs edema (n=2 [15%]) and headache (n=2 [15%]). All these events were grade 1. Importantly, no bleeding or atrial fibrillation events were observed. Image:Summary/Conclusion: Our preliminary data indicate that combination therapy of acalabrutinib plus obinotuzumab induces remissions with a major reduction in bone marrow disease after 6 months of combination therapy. Longer treatment and follow-up is warranted to determine the durability of responses after therapy discontinuation.